特殊工况下换流变零序差动保护误动机理分析及对策研究

针对高压直流输电工程中换流变压器零序差动保护误动的案例,分析了特高压换流变中性线上电流互感器在长时间单极-大地运行伴随交流系统高阻故障工况下饱和机理。采用基于工程实际参数的特高压直流输电模型进行仿真分析,揭示换流变零序差动保护误动原因。并根据区内、外故障时保护两侧自产零序电流和中性线零序电流极性差异,提出一种基于S变换相位差的换流变零序差动保护闭锁新判据,以解决特殊工况下换流变零序差动保护误动的问题。通过仿真验证该判据的有效性。

Mechanism and countermeasures of mal-operation of converter transformer zero-sequence differential protection under special conditions

Aiming at the cases of mal-operations of zero-sequence differential protection of converter transformers in the HVDC transmission project, the saturation mechanism of current transformers on the neutral line of the UHVDC converter transformer under long-term unipolar-earth operation accompanied with high-impedance fault conditions of AC system is analyzed. The reason of the mal-operations of the zero-sequence differential protection is revealed based on the UHVDC model, which adopts the actual engineering parameters. According to the polarity difference between the self-produced zero-sequence current and the zero-sequence current on the neutral line on both sides of the protection under internal and external faults, a novel blocking criterion of zero-sequence differential protection for converter transformers based on S-transform phase angle difference is proposed to solve the mal-operation of the zero-sequence differential protection under special conditions. The validity of the criterion is verified by simulation tests. This work is supported by National Natural Science Foundation of China (No. 51607106) and Open Foundation of Hubei Provincial Key Laboratory for Operation and Control of Cascaded Hydropower Station (China Three Gorges University) (No. 2018KJX05).